This is one of those strange questions that I get asked on a fairly regular basis.
I didn't understand why it was necessary at first until I was told the reason.
Apparently, in some countries, if you import a car, they want to know everything about it
including the engine number so they can make sure it's not stolen or using stolen parts.
Hahahahaha *cough* *cough*, aaaahahaha, *breathe* hahahaha. Good one.
On most engines on other cars, you can either see the number very easily, see it with a mirror
or use a piece of paper and a pencil to take a rubbing of it. Not on the smart.
OK, it might not be as drastic as that but you will have to lower the engine a lot.
The problem is that the number isn't engraved or stamped. It's laser etched.
That means you have to do a lot of cleaning to be able to see it clearly enough.
Eventually this page will cover more model but for now, it only covers...
As you look in the engine bay, its on the engine block directly behind the throttle body.
It's right next to the starter motor (which is a pain in the arse to get to as well).
This is the engine from the other side. The number is also quite small.
It's also very shallow so get your wire brush out and start cleaning. If you are lucky, you might find it.
However, it might be easier to find out from smart what the engine number should be...
...and then stamp it on the engine elsewhere for them to read. They won't know it's not the real one.